A liquid-liquid separator is used in solution polymerizations to separate the solvent and unreacted monomers (in a solvent-rich stream) from the polymer (in a polymer-rich stream). The degree of separation is influenced by the process conditions, such as, for instance, the amount of anti-solvent (e.g., propane), the amount unreacted monomers in the inlet stream, the inlet stream temperature, and the adiabatic pressure drop into the separator. However, the degree of separation is typically not realized, until undesirable polymer carry over is detected in the solvent recovery downstream equipment. Thus, there is a need for a method to determine the degree of separation of solvent and unreacted monomers from the polymer, early on, in the “work-up process” of polymer solution, and which would allow for the on-line adjustment of polymerization conditions to improve the degree of separation.
Polymerization processes and/or polymer separation processes are disclosed in the following references: International Publications,WO2012/156393,WO2002/034795, WO2011/008955; US2012/0277392; Zhang et al., Phase Behavior, Density, and Crystallization of Polyethylene in n-Pentane and in n-Pentane/CO2 at High Pressures, Journal of Applied Polymer Science (2003), Vol. 89, 2201-2209; Ehrlich et al., Phase Equilibria of Polymer-Solvent Systems at High Pressures Near Their Critical Loci: Polyethylene with n-Alkanes, Journal of Polymer Science (1963), Part A, Vol. 1, 3217-3229; De Loos et al, Liquid-liquid Phase Separation in Linear Low Density Polyethylene-Solvent Systems, Fluid Phase Equilibria (1996), 117(1-2), 40-7; Buchelli et al., On-Line Liquid-Liquid Phase Separation Predictor in the High-Density Polyethylene Solution Polymerization Process, Industrial & Engineering Chemistry Research (2007), 46(12), 4307-4315.
However, the separation process of the above art does not allow for real time feedback of the degree of separation of the polymer solution into a polymer-rich stream and a solvent-rich stream. As discussed, there remains a need for a method to determine the degree of separation of solvent and unreacted monomers from the polymer, early on, in the work-up process of polymer solution, and which would allow for the on-line adjustment of polymerization conditions to improve the degree of separation. These needs have been met by the following invention.